The Contemporary Home Free standing Lamp/Light Joule Thief Technology The Contemporary Home Free standing Lamp/Light Brian P Smith Embedded Electronics Designer

The Task You are asked to design and develop either a freestanding lamp, a wall lamp or a hanging lamp suitable for either indoor or outdoor (patio/garden) use. The lamp should utilise LEDs and a USB or solar cell power source. We are particularly keen to see ideas which explore different ways of controlling lights from simple on/off to more complex remote control. We would like this new range to be called “SOMMAR” which translates to “Summer” and will need to be available for our summer 2019 season. This range will need to be fresh and vibrant and appeal to a wide number of customers both in this country and abroad. We would also like your students to consider packaging in a typical IKEA style as well as any necessary assembly instructions.

LEDs (Light Emitting Diodes) - 1 LEDs are available in a wide range of colours, formats, and sizes Single colour LEDs Red, Green, Blue, Yellow, Orange, Amber, Pink, Lilac and White Bicoloured LEDs Red/Green, Green/Yellow Tricoloured LEDs RGB (Needs a microcontroller), Rainbow (contains a simple colour sequencing chip)

LEDs (Light Emitting Diodes) - 2 LEDs are available in a wide range of colours, formats, and sizes LED formats – LEDS are available in a range of ‘packages’ PTH – Pin thru hole SMD – surface mounted device

LEDs (Light Emitting Diodes) - 3 LEDs are available in a wide range of colours, formats, and sizes PTH – Pin thru hole 2mm, 3mm, 5mm, 8mm, 10mm diameters SMD – surface mounted device 2mm x 1mm, 3mm x 2mm, 4mm x 3mm, 5mm x 5mm

LED Arrangements LEDs are incredible versatile and often available in pre-made arrangements LED strips – these are made using SMD LEDs (single colour or RGB) along with protective resistors, they are powered by 5V or 12V. LED ‘Bulbs’ – these are made using SMD LEDs (single colour or RGB) along with protective resistors, they are powered by 12V or 240V (mains).

Powering LEDs LEDs need a particular voltage and current for them to work correctly. Too little voltage and they don’t light up. Too much current and they ‘burn out’ LEDs needed a voltage between 1.8V and 2.2V, white LEDs need at least 3V to operate, and between 5mA to 30mA to light up correctly, any more than that and they ‘burn out’. To protect the LED from too much current and to set the correct working voltage we use a SERIES RESISTOR , the value of which is found using OHMS LAW

Power Supplies USB Power supply Solar Cell power supply The cheapest Solar Cells generally only produce about 3V and 100mA of current under full sunlight. But that is plenty to operate LEDs.

Storing Electricity Rechargeable cells Super capacitors Simple AA (1.5V) cells can be charged up using a Solar cell, using a simple circuit: A simple 3V power supply that doesn’t use a rechargeable cell, but uses a SUPERCAPACITOR

Cells vs Super-capacitors Rechargeable cells (£2.00) Super-capacitors (£0.80) Positive points Negative points Positive points Negative points Which Technology would you choose and why?

What options are there? Power Supply LEDs You have two power supply options USB Solar Cell Which type of LED will you use: Coloured LED 5mm, 8mm, 10mm White LED 5mm, 10mm Rainbow cycling LED 5mm, 10mm You will need to select an appropriate power supply and LED for your particular situation Once that is done you will need to select a suitable storage system – super-capacitors are the recommended solution For white and colour cycling LEDs some extra electronics will be required For automatic switching on, when dark some extra electronics will be required

Automatic light switching USB powered Solar cell powered To automatically switch on/off the lighting circuit, a light sensor circuit and transistor will be required: To automatically switch on/off the lighting circuit, the solar cell is the sensor and a transistor is required:

Elec-trickery One of the issues for low voltage systems such as 1.5V AA batteries and 3V Solar Cells is that they cannot supply enough voltage to operate White or Blue LEDs effectively or efficiently. To over come that problem we can use a Joule Thief circuit, which uses electromagnetic induction to generate a high voltage from a low one – this was discovered by Michael Faraday. The basic circuit is:

STEM How it works When powered up the transistor is switched on by a current flow through the left hand coil, and creates a magnetic field. When the transistor turns on it causes the right hand coil to switch the transistor off, as a result the magnetic field collapse very quickly This causes a large induced voltage to be produced which powers the LED, that voltage only lasts a short time The transistor can now switch on again and so the process repeats many times a second. As a result the LED is lit for a short time, but 100’s of times per second, and to us it appears to be on all the time.

Lets make one! The first task is to wind our own inductor, to do this we need a small ferrite core and two 200mm length of solid insulated wire – Cat5 network cable is the best to use. Take the two strands of wire through the centre of the core Keeping the two strands together, wrap them around and through the core again Keeping the two wires together, make a few more turns through the centre Keep winding until you fit as many turns as will fit in a single layer around the core, typically 8-10 turns with thin insulated wire Clip the wire leads down. Note that we have two pairs of wires: one coming out the front, and one coming out the back, and strip off the insulation

Building the circuit board 1 1. Solder on AA Battery holder 3. Solder on the 2N4401 transistor 2. Solder on the 1K resistor 4. Solder on the LED ( two types of white available )

Building the circuit board 2 5. Solder in place your inductor coil, ensure the correct ends go into the holes marked 1 2 3 4 1 2 3 4 A 3V LED powered from a 1.5V battery – thanks Michael Faraday 6. Add a switch to your circuit using two lengths of wire into the holes marked SW 7. Add your 1.5V battery, press the switch and we have light!!!

More Elec-trickery The Joule Thief circuit will work fine with White or Blue LEDs and all the other colours as well BUT it will not operate colour cycling LEDs This is because the need 3V DC and the Joule Thief circuit produces a pulsing DC, which flashes the LEDs 1000 time per second (1KHz) approx. We can fix that problem by replacing the LED with the following circuit: The combination of the capacitor and diode smooth and rectify the pulsing DC to DC that the colour cycling LED needs to operate.

Where next? Using this information you now should be able to start to work out which systems you need to create the electronics for your “Sommar” light. You need to write up that information that is key to your particular idea along with any other requirements so they can be investigated. If anyone is considering the use of remote control you need to let me know so I can provide specific guidance on this method.